Variable Rate Irrigation (VRI) allows users to apply specific amounts of water to predefined sections of irrigated fields. In use, VRI relies upon a combination of hardware and software which determines water application patterns based on topography information, soil data maps, yield data and the like. Using VRI, the amount of water applied to each section of a field is controlled for varying crop types and soil types. Because of this, users are able to save water and fertilizer/chemical costs in their farming operations while maximizing the irrigation benefits from a given amount of water.
A key aspect of VRI is the control of water application rates/depths for specific areas of a given field. Applying VRI, there are primarily two methods for varying water application depths applied by center pivot or linear irrigation equipment. One is to vary the speed of the irrigation span thereby changing the water application depth for a segment of the field. For instance, reducing the irrigation span speed by 50% will double the water application depth beneath the entire span for a given area. The second method requires the control of sprinklers individually or in groups (zones) using hydraulic valves. Using the second method, sprinkler zones are turned on/off (pulsing) using computer software control algorithms which are able to change the water application depth within individual zones. For example, using a cycle time of 50% (sprinkler valve open for 50% and closed for 50% of time period) will reduce the water application depth for a given area by 50%.
The ability to control water application levels using either speed or sprinkler zone control is limited. With respect to speed control, changing the speed of an irrigation span for one area of a field necessarily requires that the speed of the entire length of the span be changed. Accordingly, since field soil types vary along the irrigation span, compromises must be made to best match application depths of a given area.
With respect to pulsing sprinklers, lag time between the signal to close/open a valve and when the valve actually closes/opens can be inconsistent throughout an irrigation event causing variations in water application depths. Further, cycle times are also limited based on the movement of the machine. If the off time portion of the cycle time is too long, the water application depths will be incorrect.
What is needed is a system to provide precise control of the water application depth in an irrigation system. Further, what is needed is a control system which is responsive to continual changes and which can make adjustments in the water application depth with very little lag time. Finally, what is needed is a control system which can control the water application depth under different water pressure conditions. The present invention overcomes the short comings of the prior art by accomplishing these critical objectives.